Ultraviolet (UV) communication is a form of optical wireless communication that operates in the LTV band. This band of electromagnetic (EM) radiation is located between visible light 150 and x-rays 160 in the EM spectrum 100. The location of UV in the EM spectrum 100 is shown in FIG. 1.
Based on absorption properties of LTV radiation in the earth's atmosphere, the UV band is divided into four main sub-bands. Vacuum LTV (10 nm-200 nm) 110 is heavily absorbed by oxygen molecules in the atmosphere. UV-C (200 nm-280 nm) 120 is fully absorbed by the ozone layer and only exists on the earth's surface through manmade sources. UV-B (280 nm-315 nm) 130 is partially absorbed by the ozone layer and is the primary agent responsible for sunburns. Finally, UV-A (315 nm-400 nm) 140 is not absorbed by the ozone layer and constitutes 98.7% of the UV radiation that reaches the earth's surface from the sun.
UV-C communication is preferably suited for short-range, low power networking. The inherent security also makes this technology ideal for networks that are used to communicate sensitive or personal information. The fact that UV-C does not operate in the radio frequency (RF) band allows it to be used in situations where RF communication may create interference or could be dangerous (e.g., hospitals, airplanes, refineries, chemical plants, etc.).
UV-A has more relaxed exposure limits when compared with UV-C, ranging from 300× to 13000×, depending on the UV-A wavelength. This may allow transmitters with higher powers to be used in a personal communication system. When compared with visible light, UV-A also has more relaxed laser exposure limits (up to 20×) due to the fact that the human retina is not sensitive to UV-A. UV-A maintains the security aspects of UV-C, as it also does not penetrate through walls, and penetration through regular glass is limited to wavelengths above ˜325 nm (depending on the type of glass). Special transparent filters also exist which allow UV-A to be blocked by glass all the way to the start of the visible light spectrum (˜400 nm).
With the proliferation of wireless devices, exchange of information between devices during meetings has become a common need. This data exchange must also be able to support large bandwidths, such as in the case of projecting of a corporate strategy video during a board meeting, or for rapid transfer of large confidential documents between board member smart phones or laptops. While wireless network security applications have been developed with this in mind, wireless networks will remain highly susceptible to eavesdropping as long as there is a means for an eavesdropper to intercept network traffic. This is always possible in the case of RF communications where this type of communication medium cannot be confined to a closed room, where a secure meeting generally takes place.
With the advent of new applications such as high resolution video, the need for wireless technologies to support these new high bandwidth applications has increased. However, many of the existing personal area network (PAN) technologies today (such as Bluetooth, which can achieve an expected 1-3 Mbps) lack these required data rates.
Finally, as new technologies are deployed to allow for short range indoor communication and as these technologies take advantage of new or existing frequency bands, the chance for interference of these new technologies with devices that are sensitive to RF communications may increase. This may be true in the case of equipment used in hospitals, airplanes, and chemical plants.
Technologies using 60 GHz, Terahertz, infrared 170, visible light 150 and UV spectrum have the potential for solving each of these issues or needs. It would be advantageous to share a secure spectrum by multiple devices (each with its own security requirements) while staying within the limits for safe transmission power levels and minimizing interference using a physical layer (PHY) that allows for flexible bandwidth allocation and power control.